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sparc64: Use pause instruction when available.

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In atomic backoff and cpu_relax(), use the pause instruction
found on SPARC-T4 and later.

It makes the cpu strand unselectable for the given number of
cycles, unless an intervening disrupting trap occurs.

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller
2012-10-27 23:00:41 -07:00
parent 270c10e00a
commit e9b9eb59ff
5 changed files with 62 additions and 16 deletions
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13
arch/sparc/include/asm/processor_64.h
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@@ -196,9 +196,16 @@ extern unsigned long get_wchan(struct task_struct *task);
#define KSTK_EIP(tsk) (task_pt_regs(tsk)->tpc)
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->u_regs[UREG_FP])
#define cpu_relax() asm volatile("rd %%ccr, %%g0\n\t" \
"rd %%ccr, %%g0\n\t" \
"rd %%ccr, %%g0" \
#define cpu_relax() asm volatile("\n99:\n\t" \
"rd %%ccr, %%g0\n\t" \
"rd %%ccr, %%g0\n\t" \
"rd %%ccr, %%g0\n\t" \
".section .pause_patch,\"ax\"\n\t"\
".word 99b\n\t" \
"wr %%g0, 128, %%asr27\n\t" \
"nop\n\t" \
"nop\n\t" \
".previous" \
::: "memory")
/* Prefetch support. This is tuned for UltraSPARC-III and later.